K324 / 6092 Paper 2 Data-Based Question Framework
Data-based questions (DBQ) in Paper 2 look scary because they combine reading, chemistry, and writing. But most DBQ marks come from doing a few repeatable jobs correctly.
This page gives you a scoring framework you can reuse on almost any DBQ:
Read → Extract → Decide → Write
Read the prompt and axes. Extract the evidence. Decide the chemistry job. Write with the correct command-word structure.
1) Read (don’t start answering yet)
Before you look at options or start writing:
- Circle the command word (describe / explain / suggest / calculate).
- Identify the data source: table / graph / experiment description.
- Check variables and units (especially cm³ vs dm³, time units, concentration units).
- Note any conditions (aqueous vs molten; dilute vs concentrated; temperature/pressure).
If you miss the axis units, you can write a “perfect” answer and still lose marks.
2) Extract (turn data into evidence)
DBQ answers need evidence. Evidence looks like:
- “increases from 2.0 to 8.0 (units)”
- “the gradient is steeper at the start (higher initial rate)”
- “levels off at about 40 cm³”
- “at 0.20 mol dm⁻³, the time is half of…”
Evidence rules that score
- Quote two values (with units) to prove a trend.
- Use comparative words: higher/lower, faster/slower, approximately double.
- Mention an anomaly only if it affects the conclusion.
3) Decide (what job is the mark scheme asking for?)
Most DBQ marks fall into four jobs:
- Describe a trend/pattern from the data.
- Explain the trend using chemistry.
- Calculate something using data (often with unit conversion).
- Suggest a reason/improvement using evidence.
If you do the wrong job (e.g. explain when asked to describe), you lose marks even if your chemistry is correct.
Quick fix page:
4) Write (templates that match the command word)
A. “Describe the trend”
As [X] increases from [value] to [value], [Y] [increases/decreases] from [value] to [value] (units).
If relevant: the change is rapid at first, then it levels off at about [value].
B. “Explain the trend (using the data)”
Use evidence first, then the driver chain:
Evidence: [quote trend/value].
Because [driver], therefore [particle-level change], so [observed trend].
Driver chain help:
C. “Suggest a reason / improvement”
A possible reason is [idea], because [chemistry logic tied to data], so [effect on results].
If the prompt is practical-style (“suggest an improvement”):
- Limitation → specific improvement → effect (accuracy/reliability).
- Use: Errors & Improvements (ACE).
D. “Calculate”
DBQ calculations usually test:
- unit conversion (cm³ ↔ dm³)
- moles/concentration (n = CV)
- gradients (rate from slope)
- percentage calculations (yield/purity)
Write the formula, substitute with units, then compute. Convert units before substituting.
Worked Examples (DBQ mini-cases)
Attempt each in 3–6 lines (Paper 2 length). Then compare your structure with the answer.
Example 1 (Describe + explain from a rate graph)
A student collects gas from a reaction and plots volume of gas (cm³) vs time (s). The curve is steep at first, then levels off at 40 cm³.
- Describe the pattern.
- Explain why the curve levels off.
Show Answer
1) Describe: The volume of gas increases quickly at first (steep gradient), then increases more slowly and levels off at about 40 cm³.
2) Explain: Because the reactant is being used up, therefore its concentration decreases with time, so there are fewer effective collisions per second and the rate decreases until no more gas is produced (curve levels off).
Example 2 (Explain, using the data: concentration effect)
In an experiment, the concentration of acid is increased from 0.50 mol dm⁻³ to 1.00 mol dm⁻³. The time taken to collect 20 cm³ of gas decreases from 60 s to 30 s. Explain this change using the data.
Show Answer
Evidence: when concentration doubles from 0.50 to 1.00 mol dm⁻³, the time halves from 60 s to 30 s (reaction is faster).
Because higher concentration means more reactant particles per unit volume, therefore collision frequency increases, so there are more effective collisions per second and the rate increases (shorter time for the same gas volume).
Example 3 (Calculate: n = CV with cm³ → dm³)
25.0 cm³ of 0.200 mol dm⁻³ NaOH(aq) is used. Calculate the number of moles of NaOH.
Show Answer
Convert volume: 25.0 cm³ = 0.0250 dm³.
n = CV = 0.200 × 0.0250 = 0.00500 mol.
A 30-second DBQ finishing checklist
Before you move on:
- Did I answer the command word (describe vs explain vs suggest vs calculate)?
- Did I include evidence (values/units, or a clear trend)?
- Did I include the key condition (aqueous/molten, dilute/concentrated, temperature)?
- For calculations: did I convert cm³ to dm³ where needed?
Next steps
- Exam Skills Hub: Paper 1, DBQ, definitions, and trend templates.
- G3 Pure / O-Level Chemistry: topic hubs in syllabus order.
- For graphs: Tables & Graphs (PDO).